96 ci Big Bore/Stroker build, anyone? : V-Twin Forum: Harley Davidson Forums
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Old 07-27-2010, 06:35 PM   #1 (permalink)
IronButt
 
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96 ci Big Bore/Stroker build, anyone?

Hello,
Leaning towards rebuilding the stock 80 ci Evo into a 96 ci big bore/ stroker on my FXR3. Evo cases are post 1995, which are said to be able to handle the extra bore with no issues. I've read and heard that this is the limit to which an 80 ci Evo can be bored . Ofcourse, I would doing other mods to accommodate such as compression ratio increase, hi lift cam, S&S carb, port and polish heads, 2 into 1 exhaust, valvetrain work, i.e., valve job, springs, pushrods, lifters, etc. , hi perf. clutch. Anyone done this type of work or similar to their Evo? If so, what are the pros and cons compared to alternatively similar builds? thanks in advance for any input.
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Old 07-27-2010, 09:18 PM   #2 (permalink)
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A friend of mine has a 96" Evo that he built at his shop. He used STD cases and said stock Harley Evo cases can't handle that bore. I think he said the studs get exposed on the inside edges when the cases are bored out to take the bigger jugs. My understanding is that 89" is the biggest you can safely go with stock cases, even the late model cases like yours. I think you could get 100hp out of the 89"er with the right innards. I have a 92hp 80" FXR4 and it's quick but my friend's bike is a real beast! Dependable too. The dependable part is what's hard to achieve with the stock cases. You don't want to be pulling studs.
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Old 07-28-2010, 06:55 AM   #3 (permalink)
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Mike-
Thanks for the input. It is my understanding that for the evo, an 89 ci is simply a stroker. It uses the stock 3-1/2" bore cylinders, thus no boring is required, but uses a 3/8" longer stroke to 4-5/8" -up from the stock 4-1/4 -along with stroker pistons. This set up will allow you the option to add a bigger bore later, if you decide you want to go bigger (to 96 ci).
To achieve 96 ci, you're boring the cases 1/8" while also using the 3/8" longer stroke. It is my understanding that the '99 evo cases will support the extra 1/8" bore without sacrificing durability or compromising the integrity of the cases. I guess this is where we get conflicting info. I've read and been told that the rod to stroke ratio and the bore to stroke ratio work very well in the EVO with this 96 ci setup, and it has proven to be one of the best available combinations for power and durability. Going any bigger though, it would be better to drop in an aftermarket engine to maintain durability. Maybe more research on my part is required.
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Old 07-28-2010, 07:09 AM   #4 (permalink)
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Quote:
Originally Posted by JamesButler View Post
Mike-
Thanks for the input. It is my understanding that for the evo, an 89 ci is simply a stroker. It uses the stock 3-1/2" bore cylinders, thus no boring is required, but uses a 3/8" longer stroke to 4-5/8" -up from the stock 4-1/4 -along with stroker pistons. This set up will allow you the option to add a bigger bore later, if you decide you want to go bigger (to 96 ci).
To achieve 96 ci, you're boring the cases 1/8" while also using the 3/8" longer stroke. It is my understanding that the '99 evo cases will support the extra 1/8" bore without sacrificing durability or compromising the integrity of the cases. I guess this is where we get conflicting info. I've read and been told that the rod to stroke ratio and the bore to stroke ratio work very well in the EVO with this 96 ci setup, and it has proven to be one of the best available combinations for power and durability. Going any bigger though, it would be better to drop in an aftermarket engine to maintain durability. Maybe more research on my part is required.
I did the 89" on my EVO, and its is stroker flywheels. I had truett and osbourn do the bottom end and I used my stock cylinders and S&S stroker pistons. I used Branch EVO heads, velva touch lifters, crane pushrods and Comp cams 3050. I put a super E on it and a dyna ignition. I had stock EVO cases (1989) and had no issues. Ran great and I sold it to my kid brother. A 96 would be more reliable and will last longer.
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Old 07-28-2010, 09:38 AM   #5 (permalink)
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Yeah James, this thing about the Harley Evo cases having some weaknesses at different spots is a debate that has been going on for a long time. I know the late cases like yours and mine are "supposed" to be the strongest of that line but whether they can take getting bored out 1/8" I can't say personally. I've seen pics of bored out cases where you could actually see some of the stud threads showing thru but I don't remember how big they bored them out. Just passing along what my friend says. He's been building hot Harleys for over 40 years and has a custom shop in San Jose, Ca.. And In my friend's opinion 96" is a sweet spot for Evo's cuz you can safely rev 'em up and still have good reliability. He has S&S flywheels in his engine. Good Luck.
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Old 07-28-2010, 06:52 PM   #6 (permalink)
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The 96" evo uses the stock thread stud pattern. All this talk about threads showing on a 3 5/8" bore evo oem case are just silly. If studs were exposed on oem cases they would also be exposed on aftermarket cases with stock bolt patterns, like the S&S 88" and 96" engines. Those later cases are fine for any 3 5/8" bore engine (88" or 96"). -Ed
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Old 07-29-2010, 10:27 PM   #7 (permalink)
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Ed-
thanks for the input. My builder who's been doing this build since the Shovelhead days says there are no problems with my cases, so I'm trying to get some feedback from anyone who runs the 96" big bore/stroker.
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Old 08-02-2010, 12:32 PM   #8 (permalink)
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After talking to my friend with the 96"er with STD cases and heads he said he pulled studs on his STD cases too. He said the Harley cases will hold up pretty good as long as you don't keep bangin' the rev limiter.

By the way in my last post, Econner, I didn't say that an 1/8th" over bore caused the studs to show. I said I didn't know how big the bore was on those cases.
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Old 08-02-2010, 01:03 PM   #9 (permalink)
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Hi from the Mile High City of Denver! The Guy to call is Randy @ HYPERFORMANCE in Iowa.....his nick name is the "KING OF CUBES" He has built motors up to 260 cu. in. so building a 96 and knowing what works and what doesnt.... He is the guy!
I mean this guy even makes complete Steel Cyclinders for EVO motors because we all know in the " real race world" steel cyclinders dont grow and change shape and lose compression like Aluminum does... not to mention push rods going out of adjustment as the cylinders grow!....

He also builds complete motors for the AHDRA Top Fuel and the NHRA 160 Pro Bike Class we see on TV....But 90% of his work in on Street motors that you and I mear mortals can have so much fun with!


Just go to his web site and read what this guy is all about!


king of cubes .com

515-266-6381

Remember....you don't steer the bike........YOU AIM IT !
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